Field of the Invention
The present invention relates to a structure of a semi-active mount exhibiting mount characteristics varying in accordance with application of current, and more particularly to a semi-active mount structure including a valve for opening or closing a vent hole, not only to seal a lower space of a valve spring when a plunger does not operate, thereby increasing rigidity of the valve spring, but also to open the lower space when the plunger operates, thereby decreasing rigidity of the valve spring.
Description of Related Art
To address continuing development of vehicle technologies and increasing consumer demand for low vibration and low noise, efforts to maximize ride comfort through analysis of noise, vibration and harshness generated in vehicles, namely, NVH performance, are being made.
Engine vibration generated in a specific RPM range during driving of a vehicle is transferred to a passenger compartment via a vehicle body while having a specific frequency. Phenomena exhibited due to explosion occurring in an engine have predominant influence on the passenger compartment.
To this end, an engine mount is mounted between the engine and a vehicle body in order to attenuate noise and vibration transferred from the engine while supporting the engine. Engine mounts are mainly classified into rubber mounts, air damping mounts, and hydraulic mounts.
The hydraulic mount has a structure in which a certain amount of fluid (hydraulic fluid) is sealed in an interior of the hydraulic mount, to generate a damping force in accordance with flow thereof between an upper fluid chamber and a lower fluid chamber. The hydraulic mount has an advantage in that it may be possible to attenuate both high-frequency vibration and low-frequency vibration in accordance with vehicle driving conditions.
Meanwhile, an active mount or a semi-active mount, which is capable of actively vertically moving an actuating plate, has recently been developed in order to improve vibration insulating characteristics of the hydraulic mount.
The semi-active mount is configured to control characteristics thereof in an ON/OFF manner. As such a semi-active mount, a volume-stiffness type semi-active mount or a bypass type semi-active mount is widely used. The volume-stiffness type semi-active mount is configured to control behavior of a membrane. The bypass type semi-active mount is additionally formed with a second flow passage to connect upper and lower fluid chambers such that the connection between the upper and lower fluid chambers is allowed or prevented.
In the case of a conventional bypass type semi-active mount, a nozzle plate is mounted between an insulator and a diaphragm, to divide an interior of the mount into an upper fluid chamber and a lower fluid chamber. In addition, a first fluid passage having an annular shape and a second fluid passage having a small length and a great cross-sectional area are formed at the nozzle plate.
Flow of a fluid (hydraulic fluid) is carried out in accordance with an increase or decrease in the inner volume of the upper fluid chamber occurring as the insulator is elastically deformed due to shift of load and vibration transferred from an engine. During flow of the fluid, vibration transferred to a vehicle body is attenuated.
A plunger is installed beneath the diaphragm. The plunger is vertically moved in accordance with application of electric power to a coil thereof. When the plunger moves upwards, the second fluid passage is closed. On the other hand, when the plunger moves downwards, the second fluid passage is opened.
The semi-active mount having the above-mentioned configuration operates to vary characteristics thereof in accordance with vehicle driving conditions by opening the second fluid passage, which has been closed, when the engine is in an idling state, and closing the second fluid passage during driving of the engine.
However, the conventional semi-active mount has inconsistencies in that the plunger should be firmly supported during driving of the vehicle in order to maintain the second fluid passage in a closed state because the fluid should be prevented from passing through the second fluid passage even when great shift of a power train occurs due to a bump or the like, whereas the plunger should be non-firmly (weakly) supported during idling of the vehicle because the second fluid should be easily opened.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.